diff options
Diffstat (limited to 'src/backend/commands/tablecmds.c')
| -rw-r--r-- | src/backend/commands/tablecmds.c | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c index 7ab3a511360..0866a680d7c 100644 --- a/src/backend/commands/tablecmds.c +++ b/src/backend/commands/tablecmds.c @@ -3017,8 +3017,15 @@ findAttrByName(const char *attributeName, List *schema) * SetRelationHasSubclass * Set the value of the relation's relhassubclass field in pg_class. * - * NOTE: caller must be holding an appropriate lock on the relation. - * ShareUpdateExclusiveLock is sufficient. + * It's always safe to set this field to true, because all SQL commands are + * ready to see true and then find no children. On the other hand, commands + * generally assume zero children if this is false. + * + * Caller must hold any self-exclusive lock until end of transaction. If the + * new value is false, caller must have acquired that lock before reading the + * evidence that justified the false value. That way, it properly waits if + * another backend is simultaneously concluding no need to change the tuple + * (new and old values are true). * * NOTE: an important side-effect of this operation is that an SI invalidation * message is sent out to all backends --- including me --- causing plans @@ -3033,6 +3040,11 @@ SetRelationHasSubclass(Oid relationId, bool relhassubclass) HeapTuple tuple; Form_pg_class classtuple; + Assert(CheckRelationOidLockedByMe(relationId, + ShareUpdateExclusiveLock, false) || + CheckRelationOidLockedByMe(relationId, + ShareRowExclusiveLock, true)); + /* * Fetch a modifiable copy of the tuple, modify it, update pg_class. */ |